US3370355A - Profiler - Google Patents

Description

Feb. 27, 1968 Filed June 20, 1966 E W. GRAHAM PROFILER 2 Sheets-Sheet l INVENTOR ERWIN w. GRAHAM L IATTORN EY Feb. 27, 1968 E. w. GRAHAM 3,370,355

PROFILEH Filed June 20, 1966 2 Sheets-Sheet 2 FIG.5

INVENTOR ERWIN W. GRAHAM *Q ATTORN EY United States Patent 3,370,355 PROFILER Erwin W. Graham, Willoughby, Ohio, assignor to The Pipe Machinery Company, Wickliffe, Ohio, a corporation of Ohio Filed June 26, 1966, Ser. No. 558,828 8 Claims. (Cl. 33-23) ABSTRACT OF THE DISCLOSURE The profiler herein disclosed comprises a parallelogram frame, preferably normally rectangular, of which one end frame member is fixed in position on a support, and a profile follower and scriber are mounted on the opposite end frame member in fixed relation thereto and to each other both endwise of, and in all directions transversely of, said other end frame member. The frame members are pivotally connected together at the corners of the frame for rocking about parallel axes, preferably by frictionless spring pivots.

Duplicate frames may be mounted on the same support for profiling opposite faces of a specimen concurrently and scribing the two profiles concurrently in their true relation to each other.

The profile follower is shaped and mounted so that the same surface of the point of the follower at all times engages the specimen of the surface.

This invention relates to a profiler for rapidly and accurately indicating the profile of a surface being traversed by a surface engaging follower, and particularly to a scribing profiler for scribing the profile of the traversed surface on suitable recording media.

Specifically the invention relates to a profiler for scribing in one continuous outline rapidly and with precision the entire profile of a selected cross-section of an article.

The invention is also directed to specific structural features such as the manner in which each follower and its associated scriber are supported and connected for movement in parallel paths, respectively; the arrangement of a plurailty of followers, each with its associated scriber, so that the profiles of opposite surfaces at a selected crosssection can be scribed concurrently; the parallelogram mounting of each follower and its associated scriber as a result of which the follower and scriber remain in fixed relation to each other and both the vertical and horizontal components of movement of the scriber are maintained equal to those of the follower, respectively; and the specific shape and mounting of each follower so that its tracer point follows accurately contours of extremely small radii of curvature without the scribed profile thereof being distorted by engagement with the surface of an article of some portion 'of the follower other than one preseleced tracing point.

Various other objects and advantages will become apparent from the following description wherein reference is made to the drawings, in which:

FIG. 1 is a front elevation of the profiler embodying the principles of the present invention;

FIG. 2 is a horizontal sectional view of the profiler illustrated in FIG. 1, and is taken on the line 22 thereof;

FIG. 3 is an enlarged fragmentary perspective view showing the followers and scribers and associated parts of the profiler illustrated in FIGS. 1 and 2;

FIG. 4 is an enlarged fragmentary view illustrating the adjustable mounting of one of the followers;

FIG. 5 is an enlarged h'orizontal sectional view taken on the line 55 of FIG. 3; and

FIG. 6 is an enlarged fragmentary sectional view taken 3,370,355 Patented Feb. 27, 1958 "ice on the line 66 in FIG. 2 and showing the lateral vibrating means used in the invention.

Heretofore profilers for obtaining the visual representations of the profile of a surface have been provided, but generally these are of such nature that the taking of profiles is unduly time consuming, the likelihood of distortion is quite pronounced, and the final results are dependent to a substantial extent on the skill of the particular operator.

The present profiler is one which is particularly adapted to follow and indicate and record the profile of any selected surface, to indicate and record concurrently, the profiles of opposite surfaces of an article which lie in the same cross-sectional plane, and also to accurately follow and scribe the profiles not only upper and lower surfaces of an article but also the edges of the article, even though the radii of the edges are very short and are generally upright, all with the extremely high degree of precision.

The present profiler is so arranged that specimens or articles can be profiled successively at a number of different cross-sections or surface areas without changing the position of the specimen relative to the support on which it is directly mounted.

In the case of turbine rotor and stator blades for turbojet engines and the like, the designed cross-sections of such blades may differ substantially progressively from the inner to the outer end so that a large number of profiles of cross-sections must be taken in order to determine whether or not the blade aproaches closely enough to the theoretical optimum of the design.

Accordingly, for purposes of illustration, the invention is shown as applied to a rotor blade of a turbo-jet en ine, its application to other articles being readily apparent from the illustrative example.

Referring to the drawings, the profiler of the present invention includes a heavy base plate 1 having a horizontal transverse slideway 2 on which a saddle 3 is mounted for horizontal movement forwardly and rearwardly relative to the base 1. The saddle 3 carries a pedestal 4 which is adapted to support a specimen S of which profiles at selected locations are to be taken.

For engaging and following the profile, and scribing its contour on a suitable record medium, the profiler proper, indicated generally at 5, is mounted on an upright support 6 which, in turn, is mounted on carrier 7. The carrier 7 is mounted on a suitable slideway 8 on the base 1 for movement in a horizontal path at a right angle to the path of the saddle 3. The carrier 7 is provided with an internally threaded bore 9 extending endwise thereof parallel to the guideway 8. A suitable driving screw 10 is in driving engagement with a threaded bOre 9 of the carrier 7, and has an outwardly extending shaft portion 11 mounted for rotation in a bearing 12 on the base 1. The shaft carries at its outer end a large spur gear 13 which is driven through a suitable reduction gear transmission or gear train, indicated generally at 14, by a spur gear 15. The gear 15 is on and co-rotatable with the drive shaft of a motor 16. The specific type of transmission or gearing and number of gears used is not critical, except that the transmission is a reduced speed transmission designed to drive the screw 10 at speed dependent upon the shape of the profile to be scribed. The transmission may be of the selective speed type, such as the selectively arrangeable gears of a conventional screw cutting lathe.

In the present invention it is often desirable that the scribed profile at any location be the outline of the entire cross-section at that location. Consequently, the profiler is arranged so that opposite faces of the specimen S are engaged at the same time by suitable followers and the profiles of the faces are scribed concurrently in their actual relation to each other.

In the form illustrated, the specimen S is a blade of a high speed jet turbine. It is shown as mounted with its longitudinal axis horizontal and extending parallel to the slideway 2, and with its faces generally horizontal. It may be adjusted by rotation about its longitudinal axis to the rotated position desired and secured in that position by a lock screw 17. Once it is fixed in position for taking a profile, it is not thereafter changed during the taking of the particularprofile. Generally, in connection with such specimens, the profile of the entire cross-section is to be taken at each of a number of selected locations along the length of the blade. Accordingly, a suitable micro-screw 18 drivingly interconnects the carriage 3 and slideways 2, and is operable by a hand wheel 19 so that the blade can be moved precisely to the axially adjusted positions desired, forwardly and rearwardly of the base 1.

In order to take the profile of the specimen S, followers 20 and 21 are provided, one follower being arranged so that its tracer point engages and traverses the upper face of the specimen S while the trader point of the other follower engages and traverses the under face of the specimen S upon driving of the carrier 7 in a direction longitudinally of the base 1.

It is desirable that the profile being traced by the followers 20 and 21 be recorded accurately. For this purpose, scribers 22 and 23 are employed, and are arranged to make the recordations directly on a transparent panel 24 coated with a suitable thin opaque film of material. The material is such that it can readily be scratched off cleanly and sharply by the scribers whenever they engage the same, and produce an extremely fine line of transparency corresponding in outline to the profile; for ex ample, a line of transparency of 0.0005 inch in width with clean, sharp boundaries. This type of line is produced when the scribers are held under such light contact with the treated plate surface that very light frictional forces are produced.

In the form illustrated, the panel 24 comprises a piece of glass, though other material may be used, suitably coated on its forward face with a very thin film of the material described.

A high degree of accuracy is required, both in traversing the surface of the specimen and in making the outline on the film on the glass, in order that the outline can be greatly magnified and enlarged by optical projecting and magnifying means and show extremely minute deviations in contour and dimensions; for example, errors of as little as one thousandths of an inch. I

To support the followers and scribers for accomplish; ing the foregoing ends, each follower and its associated scriber are mounted at two corners of the same end of a parallelogram frame. As shown, the follower 20 and a scriber 22 are mounted at the coners of one end of the parallelogram frame having two rigid coplanar longitudinal sides or arms 30 and 32. The follower 21 and its scriber 23 are mounted at the corners 'of one end of a parallelogram frame having two rigid longitudinal coplanar- arms 31 and 33. The arms of the frames are mounted at their other ends on the upright support 6 for rocking about parallel horizontal axes, respectively, extending forwardly and rearwardly of the base 1. I

In order to eliminate friction and reduce to negligible amounts any deviations such as might be introduced by conventional pivots of the rocking pin and bearing type, each of the arms is connected to the support 6 for rocking in a vertical plane by a conventional type of leaf spring pivot 6a, such as referred to in my copending application Ser. No. 414,104, filed Nov. 27, 1964. Regardless of the specific type of pivot means, the pivots used have their axes horizontal extending precisely forwardly and rearwardly of the base 2 and are essentially frictionless and free from play.

In order to connect each scriber in proper relation with respect to its particular follower, the following connection is made. Referring first to'the follower 20 and scriber 22, the follower 20 is secured in an upright position in a suitable supporting block 34 which is connected to the arm by a leaf spring or frictionless pivot 35 having its axis horizontal and extending parallel to the axis of the pivot 6a which connects the opposite end of the arm 30 to the support 6. The associated scriber 22 is carried on a block 36 which is connected by a pivot 37 to the arm 32 the pivots 35 and 37 being parallel and essentially frictionless. p

A rigid tie bar 38 connects the blocks 34 and 36 in fixed position relative to each other so that the tracer point of the follower 20 and the scribing point of the scriber 22 are precisely positioned at all times the same distance apart. The arms 32 and 30 are equal in length and parallel. The bar 38 is parallel to the support 6, which forms the opposite end of the frame, and the distance between the pivots 6a of the arms 30 and 32 is equal to the distance between the pivots 35 and 37 of the bar 38, so that the frame is a parallelogram. Thus, the scriber, during movement by the follower, follows a path which is parallel to, and identical with, the path of the tracer point of the follower. The vertical components of movement of the scriber as well as its horizontal components of movement are equal to the corresponding components of movement of the tracing point of the follower.

Correspondingly, the follower 21 and scriber 23 are constrained to a fixed distance apart and parallel identical paths. For this purpose a rigid C-fratme 40 is provided and disposed with its open facing toward the support 4. In the form illustrated, the C-frame comprises a pair of spaced plates 41 held in proper spaced relation by upper and lower blocks 42 at the rear of the Gimme, and upper and lower blocks 43 at the forward end of the C-frame. 7

The arms 31 and 33 are pivotally connected to the blocks 43, respectively, by suitable frictionless pivots 44 and 45, respectively, which are parallel to the pivots 35 and 37. I V

Counterweights 46 are mounted on the arms 30 to 33, respectively, each counterweight being adjustable along the length of its associated arm so as to maintain overbalances of the associated parallelogram frame in a manner to assure that the followers 20 and 21 ride with the proper degree of pressure on the surface of which they are to engage and follow for profiling.

It is desirable that the scribers 22 and 23 be rotatably adjustable about upright axes so that their scribing points point in the right direction and also that they be mounted for bodily adjustment. relative to their supports. It is important :also that they bear with the proper pressure against the coated glass panel 24.

For obtaining the desired relations, the scriber 22 is supported for adjustment in an upright direction, and

scriber 23 for adjustment horizontally endwise of the arms.-

Referring to FIG. 3, the scriber 22 is mounted in a suitable support 50 and secured therein in proper rotated positionby set screw 51. The support is welded to a suitable plate 52 which, near its upper end, has a' forwardly and rearwardly extending horizontal flange 53, and an upwardly and forwardly extending finger 54. The flange 53 provides a horizontal hinge connection having its axis 7 extending endwise of the arms, and is clamped between suitable blocks 55 and 56 by screws 57. When so clamped,

the plate is supported in spaced' relation rearwardly from the blocks 55 and 56, so that the bottom end of the plate 52 and, consequently, the scriber 22, can be swung toward and away from the panel 24 by flexure of the flange 53. The finger 54 is rigidly connected to the plate 52. A supporting block 58 is securely fastened to the block 36 and tie bar 38 and has attached thereto an arm 59. A tension spring connects the arm 59 with the finger 54 and pulls downwardly slightly on the arm 54 so as to yieldably urge the lower end of the plate 52, and therefore the scriber 22, toward and lightly against the plate with preselected pressure. As mentioned, it is desirable that the scriber 22 be movable vertically to adjusted positions. For this purpose, a block 62 is secured in fixed position on the block 58 and has a vertical dove-tail slideway 63. A complementary upright slide 64 is connected to the block 56 and cooperates with the slideway 63. The slide 64 is provided with screw threads 65 which are engaged by an adjusting screw 66, mounted in the block 62, and which screw is rotatable manually by a suitable knob 67. The block 56 is secured in fixed position on the upper end of the slide 64. If desired, the finger 59 can be mounted on the block 56 so that the tension of the spring 60 does not vary as the block 56 rises and falls. However, the amount of adjustment is very slight and usually this latter arrangement is unnecessary.

A somewhat similar arrangement is used for the scriber 23. Mounted on the outer end of the upper arm of the C-frame 40 is a block having a dove-tail slideway 71 therein extending endwise of the arms. A slide 72 is mounted in the slideway 71 and is driven by a suitable microscrew, not shown, operated by an adjusting knob 74, the screw being operable when rotated to adjust the slide 72 endwise of the arms. The slide 72 is provided at the bottom with a clamping block 75. A plate 76 carries a holder 77 in which the scriber 23 is secured adjustably by the screw 7 8. The plate 76 has a flange 79 which is clamped between the blocks and 72 and provides a hinge for permitting the plate 76 to rock about an axis extending endwise of the parallelogram frames forwardly and rearwardly. The plate 76 also has a rearwardly extending finger 80 which is connected by a tension spring 81 to a suitable arm 82 secured in fixed position on the block 70. The spring 81 thus flexes the plate about the juncture with its flange 79 so that it swings inwardly at the upper edge and disposes the scriber 23 into the proper light engagement with the glass plate or panel 24.

However, when forward and rearward edges of the specimen in the direction of moving the carrier 7 are approached, it may be necessary to change the rotated position of the followers 20 and 21 so that their tracer points can pass over the generally upright and short radii edges without undue interference because of engagement of some other parts of the followers by the specimen. For this purpose the followers are shaped and mounted in a specific manner. Since they are the same in construction and mounting, one only will be described in detail.

Referring specifically to the follower 20, as best illustrated in FIGS. 3 and 4, the follower comprises a cylindrical rod which is guided for axial movement by the walls of an upright slot in a block 91 which is securely fastened to the block 34. A leaf spring 92 is secured by suitable bolts 93 to the block 91 so as to hold the follower 20 firmly seated in the upright slot while permitting it to be moved axially and to be adjusted to diflerent rotated positions about its axis. The block 91 is provided, in spaced relation to its lower end, with a horizontal notch 94, the upper wall of which forms a downwardly facing bearing shoulder 95a. The upper end of the follower 20 is provided with a spherical head 95 and with a circumferential groove forming a neck 96 between the upper surface of the spherical head and the main body of the follower. A leaf spring 97 is disposed in the groove and extends forwardly and rearwardly thereof. At its rear end, the spring 9'! has yoke arms 98 between which the neck 96 is received. At its forward end, the spring 97 has an upwardly extending lip 99 which bears against a suitable abutment 100 on the block 91, as illustrated in FIG. 4. A fulcrum member 101 is provided in the bottom of the notch 94 and is so arranged that when the lip 99 of the spring is hearing against the surface 100, the fingers or yoke of the spring are stressed upwardly against the underside of the head of the follower 20 and yieldably hold the spherical head 95 firmly against the shoulder 95a.

With this arrangement the follower is held firmly in axial and circumferential positions, but it can be rotated about its axis by an operator without disturbing its adjustment either axially or vertically. At its lower end, the follower 20 is ground to a tracer point 102 which is coincident with the axis of the follower. A portion of the side of the follower at the lower end is ground away forming a wall 103 which is concave about an axis extending transversely of the axis of the follower 20 and which, beginning at the tracer point, is at the axis of the follower 20. The concave wall 103 extends axially of the tracer upwardly from the tracer point partway toward the opposite end of the tracer. Thus the intersections of said concave wall with planes normal to the axis of the follower are lines which are parallel to each other and parallel to the rocking axes of the arms 30 and 32. The purpose of this arrangement is to prevent any part of the tapering or conical surface 104 from striking the specimen and producing a false movement of the follower. For example, assuming the followers are in the rotate positions illustrated in FIG. 3 and are moving to the left, they will have to pass along and over the left edge of the specimen S. Obviously, as they start rounding the left edge, the sloping surface 104 would be engaged and displace the tracer point leftward from the edge surface. Accordingly, before the tracer points reach the edge,'the followers are rotated substantially 180 about their axes so that the concavity 103 faces to the right. Hence the tracer point 102 can pass over the edge and can move downwardly tracing the true profile until it passes the most leftward surface of the specimen at the cross section being profiled. Even if this surface becomes vertical for a substantial distance, the axis of the follower will be juxtaposed thereagainst, thus giving a true profile.

In order to facilitate the rotation of the followers in this position, suitable cross bores, such as indicated at 105 in follower 20, are provided, these cross bores being adequate to receive a small pin for turning the followers about their upright axes.

Obviously, for the right edge, the followers are retained in the rotated position shown in FIG. 3, and are moved to the right so as to pass over the right edge, thus eliminating any chance of binding such as would occur if they were started at a location to the right of the specimen and were moved to the left so as to cause the upright wall of the concavity 103 to approach headon and strike the right-hand edge in face-to-face relation.

It is to be noted that with the parallelogram support, the followers and scribers always retain their vertical alignment. Of course, there is a slight migration of all of them in a direction endwise of the arms 30 through 33 relative to the support 4 because the outer ends of these arms follow parallel accurate paths. This migration does not affect the accuracy of the scribed outline as the entire parallelogram supporting frame must be moved in this migrating direction in any event by the carrier 7 in order to traverse the surface being profiled.

Generally it is desirable that damping means be provided for each of the parallelogram frames, and in the illustrative example, the damping means are shown as connected to the arms 32 and 33, respectively, which carry the scribers. As best illustrated in FIG. 2, each damping means comprises a container 106 for damping fluid. Each of the arms 32 and 33 is provided with a dependent piston rod 107 which, at its lower end, carries a piston head 108 of somewhat smaller diameter than the internal diameter of the container 106. The piston head generally is positioned so that it is immersed in the damping fluid and the relation of the diameter of the head 108 to the internal diameter of the container 106, together with the viscosity of the fluid, controls the damping effect. Both of the containers 106 are carried on a suitable upright support 109 mounted on the carrier 7.

For climbing steep surfaces, it is desirable that vibration be imparted to the followers 20 and 21. Suitable vibrators, such as referred to in my co-pending applications, Ser. Nos. 414,104, filed Nov. 27, 1964, and 521,742, filed Jan. 19, 1966, are provided for vibrating the arms 7 30 and 31, respectively, which carry the followers. Each of the vibrators comprises a magnetic coil 110 having a core 111 closely adjacent one side of its associated one of the arms 30 and 31, respectively, are armatures 112, each of which is sufliciently close to its associated core piece 111 to effect the proper vibration when the coil is subjected to alternating or pulsating current. The coils 110 may be supported on a suitable support 113 mounted on the carrier 7. The rate of vibration is determined by the frequency of alternations or pulsations of the current supplied to the coils 110. 7

With the damping and vibrating described, the followers 20 and 21 can climb very steep surfaces effectively and very smoothly. Since the vibrations are transverse to the direction of rocking of the arms and rise and fall of the followers during profiling, the vibrations imparted by the coils do not prevent the followers from remaining effectively in continuous contact with the surface being traversed and do not introduce any distortion in the true profile scribed by the scribers 22 and 23.

- Having thus described my invention, I claim:

1. In a profiler, a specimen support, a carrier support, a profile follower,

a profile scriber, a carrier; I means having a surface on which the scriber scribes indieia as it moves in contact therewith; means supporting the specimen support and carrier support for relative bodily movement toward and away from each other along a predetermined path; 7 means pivotally connecting the carrier to the carrier support for rocking movementrelative thereto in a fixed plane, toward and away from the specimen sup- P connecting means connecting the follower and scriber to the carrier in fixed spaced relation to each other for movement as a unit with the carrier in paths which extend in opposite directions transversely of said predetermined path and which are parallel to said plane, and including constraining means constraining the follower and scriber at all times during their said movement to move concurrently each in the same direction as the other, and each in a path spaced from, parallel to, and identical in size and shape with the path of the other;

characterized in that means connect the follower to the connecting means normally in fixed position, but for manual rotation about a predetermined axis parallel to said plane to preselected rotated adjusted positions, the follower has a tracer point coincident with said axis, the follower has a wall which extends from the tracer point partway toward the axially opposite end of the follower, and which is concave outwardly from said axis, and which, at saidtracer point, terminates radially inwardly of the follower at said predetermined axis.

2. The structure according to claim 1 wherein the follower has a spherical surface at the end opposite the tracer point, said point and surface are coaxial, the end frame member on which the follower is mounted has a shoulder facing toward and engaging said surface, and yieldable means yieldably urges the follower toward said shoulder and yieldably holds said spherical surface against said shoulder.

3. In a profiler, a specimen support, a profile follower, a profile scriber, I means having a surface on which the scriber scribes indicia as it moves in contact therewith; a carrier, support means supporting the specimen support and carrier for relative bodily movement toward and away from each other along a predetermined path; a frame comprising a first end frame member, a second end frame member, and two side frame members,

said frame members being mounted on the carrier with the first end frame member in fixed position relative to the carrier, said side, frame members being connected to the end frame members at the corners of the frame for free rocking of the members relative to each other about parallel axes in paths in a fixed plane normal to said axes, and which axes, at their intersections with said plane, define the apices of a parallelogram; characterized in that the follower and scriber are mounted on the second end frame member with their axes in fixed position relative thereto and to each other, both endwise of, and in all directions transversely of, the second end frame member, and further in that a second frame comprising a first end frame member, a second end frame member, and two side frame members is mounted on said carrier with the first end frame member of the second frame in fixed relation to the carrier, the side frame members of the second frame are connected to its end frame members at the corners of the second frame for free rocking relative to each other about parallel axes, respectively, a follower and scriber are mounted on the second end frame member of the second frame with.

their axes in fixed position relative thereto and to each other, both endwise of, and in all directions transversely of, the second end frame member of the second frame; V the piovtal axes of the second frame define at their intersections with said plane the apices of a parallelogram positioned with its rocking axes parallel to those of the first frame;

the rocking axes of the first end frame members of the respective frames are spaced apart fromeach other in the direction of the width of the frames and are so arranged that the side frame members of one frame alternate with the side frame members of the other frame in the last mentioned direction.

4. The structure according to claim 3 wherein the supporting means support the specimen support and'carrier so that said predetermined path is lineal and extends endwise of the frame.

5. The structure according to claim 3 wherein counterbalance means are provided on each frame andsubstantially counterbalance the weight of said scriber, follower, the second end frame member, and the side frame members thereof.

6 The structure according to claim 3 wherein said frames are co-planar, the followers of the frames point toward each other and are aligned with each other so as to contact concurrently, respectively, those surface areas of a specimen which are directly opposite to each other in a direction parallel to the end frame members.

7. The structure according to claim 3 wherein said frame has a length greater than twice its width.

8. In a profiler,

, a frame comprising a first end frame member, a second end frame member, and two side frame members, said frame members being mounted on the carrier with the first end frame member in fixed position relative to the carrier, said side frame members being 7 connected to the end frame members at the corners of the frame for free rocking of the members relative to each other about parallel axes in paths in a fixed plane normal to said axes, and which axes, at

their intersections with said plane, define the apices of a parallelogram;

characterized in that the follower and scriber are mounted on the second end frame member with their axes in fixed position relative thereto and to each other, both endwise of, and in all directions transversely of, the second end frame member, and further in that a second frame comprising a first end frame member, a second end frame member, and two side frame members is mounted on said carrier with the first end frame member of the second frame in fixed relation to the carrier, the side frame members of the second frame are connected to its end frame members at the corners of the second frame for free rocking relative to each other about parallel axes, respectively, a follower and scriber are mounted on the second end frame member of the second frame with their axes in fixed position relative thereto and to each other, both endwise of, and in all directions transversely of, the second end frame member of the second frame;

the pivotal axes of the second frame define at their intersections with said plane the apices of a parallelogram positioned with its rocking axes parallel to those of the first frame;

and further characterized in that as to one frame, the

second end frame member is C-shaped and open endwise of the frame in a direction away from said first end frame member and toward the specimen support so that the specimen support can pass between the arms of the C, the rocking axes of the second end frame member are near the outer ends of the arms of the C, and the follower and scriber are adjacent said outer ends.

References Cited UNITED STATES PATENTS 743,980 11/1903 Forbes 3325 2,067,962 1/ 1937 Zwick 90-62 2,316,483 4/ 1943 Williams 33--23 2,351,452 6/1944 Pash 3324 2,621,556 12/1952 Beardsley et a1. 33174 X 2,648,912 8/1953 Osgood 33174 2,844,879 7/1958 Roeger 33174 3,100,344 8/1963 Sharp 3323 X FOREIGN PATENTS 380,153 9/1923 Germany.

958,662 5/ 1964 Great Britain.

HARRY N. HAROIAN, Primary Examiner.

25 LEONARD FORMAN, Examiner,

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